Typically, doors or barriers such as garage doors and industrial doors are driven to the open and closed positions by a door operator device that uses an electric motor. If the power should fail, then the door may need to be opened and/or closed manually.
Typically but not exclusively, the doors are roller doors and the door curtain is wound onto or off a curtain drum mounted above the doorway. Thus, the door operator, including the electric motor, is mounted above the doorway to drive connect with the curtain. For a person to manually reach the door operator to effect local manual operation at the operator is difficult due to the elevated position of the operator. This problem is exacerbated with industrial doors as the operator is typically some three meters or more off the floor.
It has been known to provide the operator with a drive wheel which can be manually rotated in the event of power failure to permit manual opening and closing of the door. The drive wheel is typically manually rotated by a person pulling an endless chain that extends over the drive wheel. A clutch mechanism is provided to release drive connection with the drive wheel and the door during normal motor driven operation of the operator. The clutch therefore prevents unwanted rotation of the drive wheel during normal operation of the motor, which in turn, prevents the endless chain from otherwise moving uncontrollably and becoming entangled with any building structure or with personnel. Thus, if the power should fail, the clutch needs to be engaged to permit a drive connection with the drive wheel. Numerous clutch systems have been devised but each has its own attendant disadvantages. A common problem with the clutch mechanisms is to ensure safety of operation at all times. For example, if the clutch should accidentally engage during normal motor driven operation of the motor, the drive wheel will be rotated which, in turn, will cause the endless chain to move uncontrollably and this has the aforementioned safety issue with regard adjacent structures and/or personnel. Some clutch mechanisms require the manual operation of a clutch arm to effect drive engagement or disengagement with the manually operable drive wheel. This usually requires a further user reachable chain or a cord to connect with the clutch operator mechanism. In some cases, the drive wheel is provided with an automatic mechanism to effect clutch drive engagement once the drive wheel is initially rotated. Such clutch mechanisms operate by causing a lateral movement along the longitudinal central axis of the drive wheel to displace a clutch and/or the drive wheel in a direction along the longitudinal axis of the drive wheel. Such clutch mechanisms have not always been reliable.
There is a need for improved clutch mechanism associated with a door operator device of this type.